SSRT5954 rev.5 - HP-UX TCP/IP Remote Denial of Service (DoS)

NOTICE:
There are no restrictions for distribution of this Security
Bulletin provided that it remains complete and intact.

The information in this Security Bulletin should be acted upon
as soon as possible.

INITIAL RELEASE:
24 July 2005

POTENTIAL SECURITY IMPACT:
Remote Denial of Service (DoS)

SOURCE:
Hewlett-Packard Company
HP Software Security Response Team

VULNERABILITY SUMMARY:
A potential security vulnerability has been identified with HP-UX
running TCP/IP (IPv4). This vulnerability could be remotely
exploited by an unauthorized user to cause a Denial of Service
(DoS).

Certain network traffic can result in a Denial of Service (DoS)
for HP-UX systems running TCP/IP (IPv4). Receiving a certain
packet on any open TCP/IP connection can result in a Denial of
Service (DoS) condition which can only be corrected by a reboot of
the affected system. The Denial of Service (DoS) is characterized
by high cpu utilization and a lack of response on any I/O port
including the system console.

Until patches are available to resolve the issue the Denial of
ervice (DoS) can be avoided by setting the ip_pmtu_strategy
parameter to either 0 or 3.

Discussion of ip_pmtu_strategy
----------------------------------

The default value for ip_pmtu_strategy is 1. This allows for PMTU
discovery. Once the issue of this Security Bulletin has been
resolved via patches the ip_pmtu_strategy value of 1 will again be
the preferred setting for most situations.

The ip_pmtu_strategy values of 0 and 3 set the PMTU to a fixed
size for destinations which are not on the local network.

->The ip_pmtu_strategy value of 0 sets the PMTU to 576 bytes.

->The ip_pmtu_strategy value of 3 sets the PMTU to 1500 bytes.
->This will generally result in more efficient transmission than
->the 576 byte PMTU.

->Note: For IPv4 the Next-Hop MTU may be as low as 68 bytes.
-> Therefore setting ip_pmtu_strategy=0 or 3 may cause
-> connections to stall.

Any existing connection presents the potential for a Denial of
Service (DoS). Because of this it is recommended that the
/etc/rc.config.d/nddconf be modified as discussed below and the
system be rebooted.

Note:
It has been recommended in several places including HP-UX
Bastille, System Health Check, and the Security Bulletin
HPSBUX0001-110 that ip_pmtu_strategy be set to 1. This
recommendation was made to avoid issues with which
occurred when ip_pmtu_strategy was set to 2. The value 1
was recommended because it is the system default and
for most situations results in the best performance. However,
the values 0 and 3 also avoid the issues which occurred when
ip_pmtu_strategy was set to 2. As mentioned above once the
issue of this Security Bulletin has been resolved via patches the
ip_pmtu_strategy setting of 1 will again be the preferred setting
for most situations.

Note:
There is a defect that will cause "ndd -c" to fail if there are
more than 10 directives in /etc/rc.config.d/nddconf. That defect
is fixed in the following patch:

B.11.11 - PHNE_25644 or subsequent
RESOLUTION:
->Patches are available for the core TCP/IP product for B.11.11
-> and B.11.23 from < http://itrc.hp.com>:

-> For B.11.11 - PHNE_33159 or subsequent
-> For B.11.23 - PHNE_32606 or subsequent
-> Binary files are available for B.11.22 as discussed in
-> HPSBUX01164.

->Until patches are available for the IPSec product for B.11.11
->and B.11.23 the issue can be avoided by setting
->ip_pmtu_strategy parameter to 0 or 3.

->Procedure to set ip_pmtu_strategy for B.11.22 or the IPSec
->product on B.11.11 and B.11.23
=======================================

Edit /etc/rc.config.d/nddconf to add the following:

TRANSPORT_NAME[n]=ip
NDD_NAME[n]=ip_pmtu_strategy
NDD_VALUE[n]=0

or

TRANSPORT_NAME[n]=ip
NDD_NAME[n]=ip_pmtu_strategy
NDD_VALUE[n]=3

where 'n' is the next available index value as described in the
nddconf comments.

This value will take effect when the system is rebooted.
Until the system can be rebooted use the following command
to read the /etc/rc.config.d/nddconf file and set the tunable
parameters:

/usr/bin/ndd -c

The ip_pmtu_strategy parameter can be displayed by the following
command:

/usr/bin/ndd -get /dev/ip ip_pmtu_strategy

Note: Since open connections will remain potentially vulnerable
until they are closed and certain internal data structures
are released it is recommended that the system be rebooted.

The binary files and patches cited in the HPSBUX01164 Security
Bulletin will NOT resolve the issue of this Security Bulletin in
the case of the IPSec product.

BULLETIN REVISION HISTORY:
Revision 0: 24 April 2005
Initial release

Revision 1: 25 May 2005
The binary files of HPSBUX01164 will resolve the issue for
B.11.11 and B.11.23.

Revision 2: 1 June 2005
The binary files of HPSBUX01164 will resolve the issue for the
core TCP/IP in B.11.11, B.11.22, and B.11.23.
The binary files of HPSBUX01164 will resolve NOT resolve the
issue for IPSec.
B.11.00 and B.11.04 are NOT vulnerable.
The recommended workaround is to modify
/etc/rc.config.d/nddconf and reboot.

Revision 3: 27 June 2005
PHNE_33159 is available for B.11.11.

Revision 4: 10 July 2005
PHNE_32606 is available for B.11.23.

Revision 5: 24 July 2005
Corrected description of PMTU to note that the MTU
may as low a 68 bytes.
The action for B.11.11 and B.11.23 core TCP/IP is
to install patches. For B.11.22 the action is to install
preliminary binary files.
Clarified the Resolution and Manual Actions sections.

SUPPORT: For further information, contact normal HP Services
support channel.

REPORT: To report a potential security vulnerability with any HP
supported product, send Email to: security-alert@hp.com. It is
strongly recommended that security related information being
communicated to HP be encrypted using PGP, especially exploit
information. To obtain the security-alert PGP key please send an
e-mail message to security-alert@hp.com with the Subject of
'get key' (no quotes).

System management and security procedures must be reviewed
frequently to maintain system integrity. HP is continually
reviewing and enhancing the security features of software products
to provide customers with current secure solutions.

"HP is broadly distributing this Security Bulletin in order to
bring to the attention of users of the affected HP products the
important security information contained in this Bulletin. HP
recommends that all users determine the applicability of this
information to their individual situations and take appropriate
action. HP does not warrant that this information is necessarily
accurate or complete for all user situations and, consequently, HP
will not be responsible for any damages resulting from user's use
or disregard of the information provided in this Bulletin. To the
extent permitted by law, HP disclaims all warranties, either
express or implied, including the warranties of merchantability
and fitness for a particular purpose, title and non-infringement."

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